The ability to produce pressure gain by a confined, intermittent combustion process (ideally constant-volume combustion) is a significant principle for improving gas turbine efficiencies. Indeed, the earliest working gas turbine around 1908, known as the Holzwarth engine, had valved and pulsating combustion chambers operated on a controlled explosive combustion process. However, ineffective utilization of wave action in the combustion chamber resulted in the non-uniform outflow and poor overall thermal efficiency. Holzwarth's design was surpassed by gas turbines that employed nearly constant-pressure heat addition, and newly developed compressor technology. Later, German scientists exploited pulsed combustion and wave action in the pulse-jet engine that powered the V-1 Buzz Bomb in World War II. Thereafter, theoretical and experimental efforts on various designs of pulse combustors for gas turbines have yielded limited gains, and integration with steady-flow machinery has been challenging. Recent efforts to develop pulse detonation engines (PDE) for propulsion applications has raised interest in all pressure-gain concepts, but the integration issue remains difficult for gas turbines.
Conventional steady-flow combustors are inherently subject to a pressure loss with addition of thermal energy, although ideally constant pressure. Cyclic constant-volume combustion can provide pressure gain, which boosts engine performance by effecting a more efficient thermodynamic cycle known as the Humphrey cycle. This is illustrated in FIG. 1, comparing schematic temperature-entropy (T-s) diagrams of a conventional Brayton engine (1-2-3b-4b) and the replacement Humphrey cycle (1-2-3-4) for fixed turbine inlet temperature and compressor discharge pressure. Pressure loss in conventional combustors (P3b<P2) is substituted with pressure to gain combustion process (P3>P2), enabling greater turbine power output and higher cycle efficiency for the same combustion energy input.
Comparison of ideal entropy generation during combustion for the two cycles is revealing. Air-cycle calculation with constant specific heat ratio of 1.333 shows the ratio of entropy production for the Brayton and Humphrey cycles is 0.75, the inverse of the specific heat ratio. This 25% ideal reduction in entropy production represents substantial potential over years of effort to improve the efficiency of turbomachinery components, making the pressure-gain combustion concept a revolutionary improvement for modern gas turbines. Constant-volume combustion can be achieved by both deflagrative and detonative combustion modes. While deflagrative combustion in a closed system at roughly constant volume is commonly achieved in piston engines, the use of detonative combustion in an intermittently open-system to achieve constant volume combustion has recently received significant attention. Specifically, pulse detonation engines (PDE) have been designed to create simple direct-thrust propulsion systems. In a PDE, detonable mixtures of fuel and air are admitted into open-end tube(s) and ignited, generating a detonation that provides a pulse of pressure and thrust. Following early work on single-tube PDE, recent work has focused on multiple tube PDE designs that provide more continuous but still unsteady output. Among various possible configurations is the rotary-valved multiple-tube PDE proposed by Bussing. In this design, several stationary detonation chambers are arranged circularly and coupled to an air/fuel duct via a common rotary valve. Such arrangements allow some of the PDE chambers to be filled while detonation occurs in other PDE chambers.
Various embodiments of the inventions described herein provide novel and nonobvious improvements of the incorporation of pulsed combustions and wave action combustion into steady-flow machinery.